The hypertriglyceridemia commonly associated with type II diabetes is of concern because of its possible role in the etiology of the greatly increased cardiovascular disease in this disorder. Moreover it has not been established how therapy of diabetes, especially using oral hypoglycemics, influences lipoprotein metabolism and lipase activities. This study compares VLDL metabolism, FFA metabolism in lipoprotein lipase activities in type II diabetics before and after therapy with the oral hypoglycemic agent tolinase. Results show that elevation in plasma free fatty acids in type II diabetics is caused by both increased production and impaired removal of free fatty acids. The latter was related closely to glycemic control suggesting there may be impaired reesterification of free fatty acids in uncontrolled diabetes. The results also showed that improvement of glycemic control was followed by significant falls in VLDL-TG and LDL cholesterol but no changes in HDL and HDL subfractions. The treatment of glycemia appeared to have independent effects on the metabolism of VLDL triglyceride and VLDL apoB, since in the former the transport was decreased after treatment whereas for the latter transport was unchanged whereas fractional catabolic rate increased.